In recent years, for the purpose of digitally handling image data and transmitting and storing information with a high efficiency at that time, after the MPEG (Moving Picture Experts Group) system utilizing the redundancy peculiar to image data and compressing it by a discrete cosine transform (DCT) or other orthogonal transform and a motion compensation, encoding apparatuses and decoding apparatuses based on the H.264/AVC (Advanced Video Coding) and other encoding systems (method) having a higher compression ratios have been spreading in both distribution of information by broadcast stations etc. and reception of information in general homes.
At present, efforts are being made for standardization by adding a function of scalability to this H.264/AVC, that is, SVC (Scalable Video Coding). The present specifications of SVC are put together in the JSM (Joint Scalable Video Model).
In an SVC encoding device, an input image is separated into for example two layers of an upper layer and a lower layer by an image layering circuit. Thereafter, the upper layer is encoded by an upper layer encoding circuit, and the lower layer is encoded by a lower layer encoding circuit. Then, the encoded upper layer and lower layer are multiplexed and transmitted.
The lower layer is also called a “base layer” and is a layer of a low quality. When decoding only the bit stream of the lower layer, an image having a relatively low quality is decoded. The lower layer includes more important information as the quality.
The upper layer is also called an “enhancement layer” and is a layer for enhancing the quality and decoding a high quality image. When decoding the bit stream of the upper layer in addition to the bit stream of the lower layer, it is possible to decode a higher quality image.
In the encoding apparatus explained above, when the upper layer encoding circuit performs intra-coding, it is possible to use the decoded image obtained by encoding, then decoding at the lower layer encoding circuit as a predictive image.